Excitation energy dependence of the photoluminescence from self-trapped excitons in halogen-bridged mixed-valence platinum complexes

Abstract

The excitation energy dependence of the photoluminescence (PL) of self-trapped excitons has been investigated in [Pt(en) 2][Pt(en) 2Cl 2(1− x) Br 2 x ](ClO 4) 4 ( x = 0, 0.08, 0.15) single crystals. The peak energy of the PL shifts to higher energy with increasing excitation photon energy from 2.4 to 2.6 eV. When the excitation energy is above 2.6 eV, the position of the peak energy is independent of the excitation energy and becomes almost constant. The magnitude of the peak energy shift increases with the molar fraction of bromine. These results are well understood by the distribution of the electron-hole separation which may depend on the excitation energy.